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Linux in a Nutshell

This directory of Linux commands is from Linux in a Nutshell, 5th Edition.

Click on any of the 687 commands below to get a description and list of available options. All links in the command summaries point to the online version of the book on Safari Bookshelf.

Buy it now, or read it online on Safari Bookshelf.


file [options] files

Classify the named files according to the type of data they contain. file checks the magic file (usually /usr/share/magic) to identify some file types.



Brief mode; do not prepend filenames to output lines.


Check the format of the magic file (files argument is invalid with -c). Usually used with -m.

-f file

Read the names of files to be checked from file.


Follow symbolic links. By default, symbolic links are not followed.

-m file

Search for file types in file instead of /usr/share/magic.


Flush standard output after checking a file.


Check files that are block or character special files in addition to checking ordinary files.


Print the version.


Attempt checking of compressed files.

Many file types are understood. Output lists each filename, followed by a brief classification such as:

ascii text c program text c-shell commands data empty iAPX 386 executable directory [nt] roff, tbl, or eqn input text shell commands symbolic link to ../usr/etc/arp


List all files that are deemed to be troff/nroff input:

file * | grep roff

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